A couple of months after Sanofi $SNY and Alnylam $ALNY retooled their RNAi collaboration so that the French pharma giant could concentrate on their hemophilia therapy while giving up rights to the biotech’s patisiran, the two partners are also going their separate ways on a late-stage drug for rare cases of primary hyperoxaluria type 1.

Sanofi is taking a pass on an option for lumasiran (ALN-GO1), leaving Alnylam CEO John Maraganore to take the drug into Phase III with a brand new breakthrough drug designation from the FDA to speed things along.

Their drug is designed to “reduce the hepatic levels of the GO enzyme, thereby depleting the substrate necessary for oxalate production,” which triggers severe adverse events often leading to kidney failure. And Alnylam is in competition with Dicerna $DRNA, a blood rival which is going after a different target in treating the same disease.

Sanofi may have all the R&D action it wants right now. After leaving the market hanging on promises of a major new deal to assist the struggling pharma giant, Sanofi acquired Bioverativ for $11.6 billion and quickly followed with its acquisition of Ablynx. The Bioverativ deal helped explain Sanofi’s interest in gaining the worldwide rights to Alnylam’s fitusiran, giving it a bigger pipeline of hemophilia therapies.

Alnylam didn’t sound in any way aggrieved today, happy to collect their third BTD from the agency and another Phase III candidate as they prep what is widely expected to be a near-term approval for patisiran, now under review.

“Based on Phase I/II clinical data presented to date, we believe lumasiran could be a transformative treatment for patients with PH1, an ultra-rare disease with no approved therapies, in which excess oxalate production leads to kidney failure and significant morbidity and mortality,” said Yvonne Greenstreet, the COO at Alnylam. “We are also thrilled with FDA’s decision to grant Breakthrough Therapy Designation to lumasiran. We believe this is a testament to the drug’s potential to address the severe unmet medical need that PH1 represents for patients and their families. Alnylam is now poised to advance lumasiran into Phase 3 in late 2018 and, assuming approval, to commercialize lumasiran globally.”